Parents, Where do you draw the privacy line?

if my child had given me a reason to question their integrity in the past........I d check things of theirs out randomly.......and I ve done it with my kids..........yep.....there was some complaining about it......I have a simple rule "if you have nothing to hide........you have nothing to fear"...May sound harsh....but if theres going to be a problem with trust.....its kind of game on at that point.